Socioeconomic deprivation and survival outcomes in patients with colorectal cancer

Abstract

Socioeconomic deprivation has been linked to detrimental healthcare outcomes. We sought to examine whether patients with colorectal cancer (CRC) from socioeconomically disadvantaged areas experience worse survival outcomes and how it interacts with other factors. In this population-based study, patients with CRC diagnosed between 2007 to 2015 in the SEER program were reviewed. Socioeconomic deprivation was measured using the Area Deprivation Index (ADI) linked to patients' residence addresses. The effect of ADI on cancer-specific survival and overall survival was evaluated using survival analysis. The Inverse Probability of Weighted (IPW) method and multiple regression was performed to account for the confounding bias. Subgroup analyses were used to test interactions. Multiple mediation analysis was used to estimate the mediating effects. Overall, 266,620 eligible patients were included in further analyses. Compared with low ADI patients, high ADI patients had more unfavorable characteristics and worse cancer-specific (hazard ratio [HR] 1.14, 95% CI 1.12-1.16, P<.001) and overall survival (HR 1.11, 95% CI 1.09-1.12, P<0.001). The results were similar after accounting for confounding factors using the IPW and multiple regression methods. Subgroup analyses revealed the relative robustness of ADI as a prognostic factor. They detected significant interactions between ADI and other covariates on cancer survival, such as age, race, insurance status, disease stage, and receipt of treatment. Multiple mediation analyses identified several factors mediating survival disparities, including anticancer therapy, insurance status, race, marital status, and age. This study suggested that high ADI CRC patients were associated with more unfavorable characteristics at presentation and lower cancer and noncancer survival after treatment than their low ADI counterparts. Multiple factors interacted and mediated these survival disparities associated with the ADI.

Keywords: SEER program; Socioeconomic deprivation; area deprivation index; cancer survival; colorectal cancer; neighbourhood disadvantage.

Figure 1

Patient selection diagram. Abbreviations: CRC, colorectal cancer; SEER: Surveillance, Epidemiology, and End Results; ADI: Area Deprivation Index.

Figure 2

Crude Kaplan-Meier survival curves stratified by ADI for cancer-specific survival (A) and overall survival (B); IPW-adjusted Kaplan-Meier survival curves stratified by ADI for cancer-specific survival (C) and overall survival (D). Abbreviations: ADI: Area Deprivation Index; IPW: Inverse Probability of Weighting.

Figure 3

The covariate balances between the low and high ADI groups in patients with colorectal cancer are evaluated by the SMDs. SMDs are calculated as follows: the numerator is the mean of the treated group minus the mean of the control group, and the denominator is the “pooled” standard deviation (the square root of the mean of the group variances). A difference of SMD equal to zero is an ideal balance. The blue dots are SMDs for each variable before using the IPW adjustment. The red dots are SMDs for each variable after using IPW adjustment. Abbreviations: ADI: Area Deprivation Index; SMD: standardized mean difference; IPW: Inverse Probability of Weighting.

Figure 4

Results for the subgroup analyses for cancer-specific survival are summarized in a forest plot.

Figure 5

The estimation of direct and indirect effects contributing to the disparities associated with the ADI on cancer-specific survival in patients with colorectal cancer. Direct effect is the ADI disparity on cancer-specific survival that cannot be explained by all the mediators/confounders included in the model while the indirect effect is the opposite. Abbreviations: ADI: Area Deprivation Index.